Polyurethanes are a known class of materials that have found extensive commercial application because of their excellent physical properties. These polymers are suitable for molding, spraying, and coating products where tensile strength, toughness, and impact resistance are required. In many of the established manufacturing processes it is preferred to employ a one-shot system whereby the polyisocyanate and active hydrogen compounds are converted to the final product in a single reaction step. In other known processes an intermediate product, usually called a prepolymer, is formed first by reacting a stoichiometric excess of a polyisocyanate with an active hydrogen compound, and the prepolymer is subsequently converted to the final polymer in a second reaction involving a further active hydrogen compound.
An example of polyurethane chemistry is disclosed in U.S. Pat. No. 4,686,242 to Turner et al. which teaches a process whereby an amine functional compound having an equivalent weight of at least about 400 is reacted with an excess of a polyisocyanate to form an isocyanate-terminated prepolymer, which prepolymer is further reacted with a polyol. Polymer properties were better when made via a prepolymer route as compared to a one step process (col. 1 lines 31-49). The patent also teaches that primary amines tend to react too quickly with isocyanates in a one step process, so a two step process should be used. Additionally, Turner teaches the use of sterically hindered amines in lieu of primary amines so as to control this reactivity.
Another example of urethane chemistry is set forth in U.S. Pat. No. 5,510,445 to Haider, et. al., which teaches a one step process for the formation of polyurethanes, comprising reacting at an isocyanate index of from 90 to 200 (a) diisocyanates; (b) 25 to 70 equivalent percent, relative to the total of components (b) and (c), of one or more amine-terminated polymers containing at least two aromatically bound isocyanate-reactive primary or secondary amino groups and/or aliphatically bound isocyanate-reactive secondary amino groups; and (c) 75 to 30 equivalent percent, relative to the total of components (b) and (c), of one or more aromatic diamine chain extenders having a molecular weight of from 108 to 399. This art teaches that large amounts of the amine-terminated polymers and any amine chain extenders contain exclusively aromatically bound primary or secondary amino groups and preferably also contain alkyl substituents. Moreover, Comparative Examples 7 and 8 teach that a primary amine terminated polyether is too reactive for a one step process methodology and should be avoided.
U.S. Pat. No. 5,710,230 to Steppan relates to a process for the production of polyurethane by processing the reaction mixture consisting of a diisocyanate and an isocyanate-reactive component via a one-shot process at an isocyanate index of about 80 to 130. The isocyanate-reactive component consists of 1) at least one polyol having functional groups which are hydroxyl groups, amine groups, or mixtures of hydroxyl groups and amine groups such that the equivalent ratio of hydroxyl groups to amine groups is from 0:1 to 1:1, and 2) at least one chain extender which is selected from diols, triols, primary aliphatic amines, secondary aliphatic amines, aminoalcohols and mixtures thereof. The equivalent ratio of hydroxyl groups to amine groups in the chain extender component is from 1:2 to 10:1. Steppan does not teach the use of aromatic diamines as chain extenders.
U.S. Pat. No. 5,239,041 to Grigsby teaches a process for preparing a polyurethane made from hindered polyetherpolyamine that is obtained by reacting a polyol having two or more hydroxyl groups with an effective amount of long chain alkyl epoxide to give an at least partially hindered intermediate having hydroxyl terminations; and then aminating at least one of the hydroxyl terminations on the intermediate to primary amine groups to give an at least partially hindered polyetherpolyamine. The hindered polyetherpolyamine is then reacted with a polyisocyanate. This art teaches that the long chain alkyl group provides steric hindrance to the primary aliphatic amine group, which slows down the reactivity of the amine, which is said to be useful since it allows for longer shot or flow times, which in turn permit larger parts to be made from existing equipment.